#include <bits/stdc++.h>
using namespace std;

int main(){

    int n,k;
    cin >> n >> k;

    vector<pair<int,char>> a(k); 

    for(int i=0;i<k;i++){
        int at;
        char ct;
        cin >> at >> ct;
        a[i] = make_pair(at,ct);
    }
    sort(a.begin(),a.end());

    vector<char> ans(n);
    bool check = false;
    int now=0,r=0,g=0,b=0;
    for(int i=0;i<k;i++){
        auto [at,ct] = a[i];

        if(ct == 'R'){
            while(r < (at+2)/3) {
                ans[now] = 'R';
                now++,r++;
            }
            while(g<b && g<r && now != at) {
                ans[now] = 'G';
                now++,g++;
            }
            while(b<g && b<r && now != at) {
                ans[now] = 'B';
                now++,b++;
            }
 
            while(now != at) {
                ans[now] = 'G';
                now++,g++;
                if(now != at){
                    ans[now] = 'B';
                    now++,b++;
                }
            }

        } else if(ct == 'G') {
            while(g < (at+2)/3) {
                ans[now] = 'G';
                now++,g++;
            }
            while(r<b && r<g && now != at) {
                ans[now] = 'R';
                now++,r++;
            }
            while(b<r && b<g && now != at) {
                ans[now] = 'B';
                now++,b++;
            }


            while(now != at) {
                ans[now] = 'R';
                now++,r++;
                if(now != at){
                    ans[now] = 'B';
                    now++,b++;
                }
            }

        } else {
            while(b < (at+2)/3) {
                ans[now] = 'B';
                now++,b++;
            }
            while(r<g && r<b && now != at) {
                ans[now] = 'R';
                now++,r++;
            }
            while(g<r && g<b && now != at) {
                ans[now] = 'G';
                now++,g++;
            }

            while(now != at) {
                ans[now] = 'R';
                now++,r++;
                if(now != at){
                    ans[now] = 'G';
                    now++,g++;
                }
            }

        }

        if(now != at) {
            check = true;
            break;
        }
    }

    while(now != n) ans[now++] = 'R';

    if(check) cout << -1 << endl;
    else {
        for(int i=0;i<n;i++) cout << ans[i] ;
        cout << endl;
    }
    

    return 0;
}